The present invention relates generally to mechanical devices used to cyclically flex and unflex the hip and knee joints of a human leg for rehabilitative purposes, and more particularly provides a passive motion exerciser which uniquely functions to simultaneously flex the hip and knee joints in a manner maintaining a predetermined correlation between the hip and knee joint flexure angles regardless of the length of the leg.
Passive motion leg exercising devices are well known in the medical arts and are typically utilized subsequent to leg joint surgery to slowly flex and unflex the hip and knee joints of a human leg without exertion or effort by the patient. A variety of rehabilitative benefits are derived through use of passive motion exercisers of this type. For example, such passive exercising of a hip or knee joint functions to break up scar tissue around the joint, without muscle contractions, to prevent "freeze-up" of the joint. Additionally, the use of a passive motion exercising device forces fluid motion in the joint to thereby increase blood circulation in the tissue surrounding it. Moreover, such passive exercise of the joint considerably reduces the pain level during the healing process. Because of this reduction in pain level, the necessity for pain reducing drugs is concomitantly reduced. Finally, the use of a mechanical device such as the passive motion exerciser reduces the physical therapy cost involved which arise when a physical therapist is used to manually manipulate the leg.
Conventional passive motion exercisers are typically provided with a leg suppot assembly to which a portion of the leg to be passively exercised is securable. This leg support assembly, in turn, is interconnected to a base portion of the exerciser by a suitable linkage structure. A motor within the base portion is used to drive the leg support assembly about a primary pivot point on the linkage structure to achieve the desired cyclical flexing and unflexing of the hip and knee joints.
Such conventional passive motion exercisers may generally be divided into two broad categories--those in which the primary linkage structure pivot point is alignable with the hip joint, and those in which such primary pivot point is designed to be positioned in a non-aligned, spaced relationship with the hip joint. Despite their well known rehabilitative benefits, however, each of these types of conventional passive motion exerciser is subject to a variety of equally well known disadvantages and limitations.
For example, the linkage structure on exercisers in which the primary pivot point is alignable with the hip joint typically extends along one side of the exerciser base portion and terminates at a point closely adjacent the hip joint of the leg being exercised, the other leg extending along the opposite side of the exerciser. Accordingly, to exercise the other leg, it is necessary to disassemble the linkage structure and remove it from the exerciser, and then reconnect the linkage structure to the other side of the exercising apparatus. As is well known, this can be a somewhat cumbersome, inconvenient and time-consuming procedure.
This particular problem is alleviated by exercisers in which the primary pivot point of the linkage structure is not aligned with the hip joint, but is forwardly offset therefrom. In this type of passive motion exerciser, the changeover from leg to leg is more conveniently and quickly effected. However, because the hip pivot point of the apparatus is not aligned with the exercised leg hip joint, the apparatus itself is not anatomically aligned with the leg being exercised. Because of this misalignment, the apparatus has a tendency to shift relative to the patient during its operation. Additionally, during its cyclical flexing motion, the leg support structure tends to move relative to the leg which it supports. This relative movement can cause uncomfortable abrasion of the exercised leg by the leg support structure, particularly where the exerciser is utilized for extended periods of time.
Another limitation inherent in conventional passive motion exercisers of both types is that the leg support assembly has a fixed width and depth sized to accommodate an "average" leg. This limitation can lead to patient discomfort in cases where the supported leg is appreciably thinner or thicker than average.
In addition to the foregoing limitations and disadvantages, conventional passive motion exercisers typically have a significant shortcoming relating to the heretofore unavoidable variance in the relationship between the hip and knee joint flexure angles of the supported leg when legs of different lengths are passively exercised. More specifically, in conventional exercisers leg length variances change the knee joint flexure angle resulting from a given angle of hip joint flexure so that proper "calibration" between the total exerciser stroke length and the resulting angular range of knee joint flexure is rather difficult to achieve.
It is, of course, often critical to the rehabilitative process following knee surgery that the knee joint flexure range be maintained within medically prescribed limits. To overcome the aforementioned calibration shortcoming, conventional exercisers are typically provided with a potentiometer device which actually measures the flexure angle of the knee joint. The stroke length of the exerciser must be carefully correlated, on a trial and error basis, with the potentiometer reading to achieve the desired flexure angle range for the knee joint. In other words, the conventional exerciser must be carefully "tuned" to each leg which it flexes. If this sometimes laborious calibration procedure is not carefully and skillfully executed, damage to the knee joint can easily occur.
It can be seen from the foregoing that conventional passive motion exercisers are subject to a variety of limitations and disadvantages. It is accordingly an object of the present invention to provide passive motion exercising apparatus which eliminates or substantially minimizes abovementioned and other limitations and disadvantages commonly associated with conventional mechanial leg exercisers.